140 On the Chemical Composition of Wernerite, 
the change would appear to have been effected in a manner 
different from that above described. - 
The proportion of alumina to silica is nearly 1 : 2, while in 
unaltered scapolite the quantity of silica is always rather 
less than double that of alumina. If, then, we assume that the 
absolute quantity of alumina has not been altered, the in- 
crease of silica may be regarded as the consequence of the 
introduction of silicate of magnesia.. As regards the bases, 
the difference between the composition of this mineral and 
that of unaltered scapolite consists in the large proportion 
of peroxide of iron and magnesia, with the small proportion 
of alkalies. The introduction of so large a quantity of per- 
oxide of iron would necessarily reduce the relative propor- 
tion of silica and alumina. The composition of this mineral 
therefore indicates :— 
' An absolute increase in the 
qualities of : ‘ SiO,, F,O,, Mg O 
An absolute diminution of Ca O, (KO), Na O. 
A relative increase of . rO., MeO 
A relative diminution of SiO,, Al,O,, KO, Na O Ca O. 
The nature of this change would appear to indicate cir- 
cumstances altogether different from those before assumed, 
and it serves to shew that the explanation of pseudomor- 
phic phenomena would require a much more intimate know- 
ledge of the locality in which the minerals occur than is 
often attainable. 
C. SUBSTITUTION OF LIME FOR ALKALIES. 
Epidote in the form of Wernerite (from Arendal). - 
The substance of the crystals presented all the physical 
characters of pistacite. Density 3-223. Analysis gave— 
I. II. III. 
Silica, ; 37°92 —- 37°92 
‘Alumina, . } 34-99 19:09 19-21 
Peroxide of iron, 15°55 15°55 
Lime, 22°94 22:42. 22°68 
Magnesia, . . 0:19 0-31 0°25 
Potash, ; — 0:23 23 
Soda, : oe — 0:39 39 
Water, : é 2°61". -°2*6T 2:25 
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